Light microscopic observations of the resin embedded tissue showed the affected neurons as rounded cells with the characteristic eccentric nucleus, central cytoplasmic dark granules and some vacuoles. Under the electron microscope, the central part of the cytoplasm was devoid of endoplasmic reticulum and it was filled with mitochondria of bizarre shape and of different sizes, with numerous lysosome-like structures, with several vacuoles and with small (60-80 nm) electron-dense inclusions of ragged contour and not membrane bound; these inclusions may represent glycogen deposits. The Golgi apparatus was either absent or was seen in the form of irregularly arranged cisternae or of a group of vesicles. Thiamine pyrophosphatase reaction was seen in some short cisternae or vesicles. Acid phosphatase activity was present in many of the lysosome-like structures suggesting the formation of secondary lysosomes and autophagosomes.